1. Field of the Invention
The invention is concerned with electrodeposition of polymers in aqueous dispersion onto conductive surfaces wherein the article which comprises such surfaces is the cathode in an electric current carrying loop.
2. Description of the Prior Art
The usual procedure for coating of polymers, which are dispersed in aqueous media, onto articles has been carried out by making the article to be coated the anode. Most such anodic depositions employ the carboxyl as the functional group which assists in the transport of the polymer to the electrode. There previously has been some recognition that a cathodic electro-deposition system would be desirable. However, there are also problems with the known cationic systems. In general, especially with amine and ammonium type surfactants, the known cationic methods are carried out at low pH. Corrosion of metals becomes a problem at low pH. Such a method, for example, is shown in U.S. Pat. No. 3,159,558 in which the process is carried out at a pH of from about 2 to about 6. The cations, which provide the means of transport in most of the known cationic electrophoretic systems, remain with the polymer after deposition and continue to be points of moisture sensitivity. Furthermore, in the weak base systems the pH and the conductivity are interdependent and cannot be easily varied independently.
An improved process for cationic electrodeposition, in which cation-activity is provided by a sulfonium cation, is described in Applicants' copending application, Ser. No. 128,553, filed Mar. 26, 1971, "Cationic Electrodeposition of Polymers Onto a Conductive Surface", now abandoned, of which Ser. No. 587,472, filed June 16, 1975, is a continuation. Other new cationic electrodeposition processes are described in Applicants' two applications filed on Aug. 29, 1973: "Cathodic Electrodeposition of Polymers Onto a Conductive Surface" (application Ser. No. 392,699), now abandoned, of which Ser. No. 569,715, filed Apr. 21, 1975, is a continuation-in-part wherein cation-activity is provided by reducible, nitrogen-containing cations and "Electrodeposition of Isothiouronium Stabilized Lyophobic Colloids" (Application Ser. No. 392,700) now U.S. Pat. No. 3,882,009 wherein cation-activity is provided by isothiouronium cations.